Tony Martin, the Norfolk farmer who shot a teenage boy in the back as he tried to burgle his isolated farmhouse, was yesterday found guilty of murder and sent to prison for life at the end of a case that touched a raw nerve across rural Britain.

In spite of cries of "yes, yes" and "I hope you die in jail" from the family of 16-year-old Fred Barras, the farmer - flanked by two police officers after receiving threats on his life - remained unmoved.

Martin was found guilty of murder by a jury of six men and six women who had earlier given not guilty verdicts on charges of attempting to murder another man, the burglar Brendon Fearon, and of possession of a firearm and ammunition with intent to injure life. He was found guilty of wounding Fearon with intent to kill.

Passing three sentences of life, 10 years and 12 months to run concurrently, Mr Justice Owen said: "It seems to me that this case serves as a dire warning to all burglars who break into the houses of other people.

"The law is that every citizen is entitled to use reasonable force to prevent crime. Burglary is a crime and a householder in his own home may think he is being reasonable but he may not be reasonable and that can have tragic consequences."

Martin killed Barras, a market trader from a Gypsy travelling family based in Newark, Nottinghamshire, last August during a late-night incident at his farm. The teenager, who had a number of convictions, was on his "first big job" to burgle Martin's home, Bleak House. He and Fearon were attacked by one of the farmer's rottweilers as they tried to get away.

The court heard that Martin, who had a vitriolic hatred for burglars and Gypsies, had come downstairs with a pump-action Winchester shotgun and fired at the two men.

Barras had pleaded for his life, shouting: "I'm sorry. Please don't. Mum." In panic, Fearon, who was seriously injured, pulled out a rotten window and he and Barras jumped through. It was not until the next afternoon that the teenage boy's body was found.

Norwich crown court heard that Martin - who took a 4ft teddy bear with him to court every day - had been repeatedly burgled and that he had laid booby traps and lookout posts for anyone who came onto his property.

Peter Tidey, the chief crown prosecutor for Norfolk, said: "Actions such as that taken by Tony Martin cannot be tolerated in a civilised society. When people break the law it is for the law to punish them, not for individuals to take the law into their own hands, whether acting out of revenge or their own individual system of justice."

The Barras family, who attended the court in large numbers every day, last night issued a statement saying: "As Fred's family we cannot and do not condone his actions. We are aware that he had failings and would have expected him to be dealt with and punished in the criminal justice system. He was not given that chance."

The verdict will be greeted with horror by the farmer's many supporters across the country who believed he did the right thing. Yesterday morning as he arrived in court an official passed on a handful of letters of support to add to the hundreds he received throughout the case.

A close friend of Martin, Malcolm Starr, said: "I'm absolutely devastated by the outcome and to be quite honest I think the whole country will be genuinely gobsmacked.

"If people were put away for longer for burglaries then they would not have been there and they would not have been shot."

The media agent Max Clifford, who gave Martin free advice, said last night he believed the conviction was a miscarriage of justice.

Martin's mother Hilary, 86, said it should have been the burglars in the dock and not her son. She added: "I am shocked. I am disappointed. I can't believe it. Because of this verdict decent people will not be able to sleep at night. He was merely defending himself against people who were thieves and vagabonds."